Effects of explicit tidal forcing in an OGCM on the water-mass structure and circulation in the Indonesian throughtlow region

Tidal and internal gravity waves significantly contribute to ocean mixing processes, yet these small-scale processes have been parameterized traditionally by sub-grid scale mixing schemes. With free surface methods growing in popularity in z-coordinate models it offers the option to explicitly resolve tides in such models (although sub-grid scale processes associated with tides, such as internal wave breaking, even in eddy-resolving OGCMs still have to be parameterized). The eight most important constituents of the semi-diurnal and diurnal tides have been implemented in a global version of the MOM3 GFDL ocean model. Tidal currents play an essential role in transport and mixing processes in the Indonesian Seas. The simulated long-term mean impact of tidal mixing on water-mass structures in the Indonesian Archipelago is compared with observations. Tidal rectification and associated mixing in the Indonesian Archipelago improve the agreement with observed long-term mean and seasonal pattern of sea-surface temperature (DeltaSST approximate to 0.3 degreesC) and heat fluxes (Deltaheat flux approximate to 20 W/m(2)), sea-surface salinity (DeltaSSS approximate to 0.15 psu) and subsurface properties including throughflow transports. However, regional differences exist and seem to be related to details of the bottom topography. Furthermore, as tides influence ocean properties via a model's mixing parameterization, rectification of the ocean state by tides strongly depends on the choice of sub-grid scale parameterizations. In the present model, this leads to excessive thermocline warming in the open ocean. Two examples with different mixing parameterizations plus tidal forcing are discussed. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.